Graphene oxide nanoplatelets can change the pore size and pore structure of a porous medium formed by phase inversion. The graphene oxide membrane has anti-biofouling capability due to its hydrophilicity and electrostatic repulsion characteristics. It also has superior mechanical strength and water permeability.
A commercial process for photocatalytic water splitting to produce hydrogen applies a two-photocatalyst system. The two-photocatalyst system is comprised of an H2-catalyst and an O2-catalyst to produce hydrogen gas and oxygen gas, respectively. The safety issue of an H2—O2 explosion must be considered in the commercial process. Conventionally in the Z-scheme, two catalysts are mixed in one reactor to perform photocatalytic water splitting, and thus hydrogen and oxygen are produced as a mixture. Two compartments of the twin reactor are separated by an ion-exchange membrane. Thus, a reverse reaction occurs which reduces the efficiency of water splitting. Under visible-light irradiation, hydrogen and oxygen can be separately generated.
Photocatalytic water-splitting into hydrogen gas (H2) and oxygen gas (O2) using sunlight has attracted considerable attention as a renewable energy resource. For large-scale hydrogen fuel production, powdered photocatalytic water-splitting, which has a large area for catalyst-water contact and an uncomplicated reactor design, is advantageous over photoelectrochemical systems. To make powdered photocatalytic water-splitting sustainable, a visible-light sensitive material capable of splitting water into H2 and O2 is critical. Numerous studies have reported metal-containing photocatalysts with high activity for H2 or O2 generation from water decomposition under visible-light irradiation, but most only executed water-splitting half-reactions with sacrificial reagents. Domen et al. developed Rh2-yCryO3GaN:ZnO compounds, which contain noble metals and are so far the most active catalysts for overall water-splitting under visible light irradiation (J. Am. Chem. Soc. 2012, 134, 8254). An alternative approach for cost-effective hydrogen production is the development of photocatalysts from carbon materials, which are abundant and environmentally friendly.
Graphitic carbon nitride and graphene oxide are capable of decomposing water for H2 generation if sacrificial reagents are added under irradiation. Electronic structural analysis revealed that graphene oxide materials have conduction band minimum (CBM) and valence band maximum (VBM) levels suitable for generating hydrogen gas (H2) and oxygen gas (O2), respectively, under visible-light irradiation.